Foamed thermoplastic polyurethanes

ABSTRACT

Process for the preparation of foamed thermoplastic polyurethanes characterized in that the foaming of the thermoplastic polyurethane is carried out in the presence of thermally expandable microspheres.

This application is the National Phase of International ApplicationPCT/EP00/00039 filed Jan. 5, 2000 which designated the U.S. and thatInternational Application was published under PCT Article 21(2) inEnglish.

FIELD OF THE INVENTION

The present invention is concerned with a process for the preparation offoamed thermoplastic polyurethanes, novel foamed thermoplasticpolyurethanes and reaction systems for preparing foamed thermoplasticpolyurethanes.

BACKGROUND OF THE INVENTION

Thermoplastic polyurethanes, herein after referred to as TPUs, arewell-known thermoplastic elastomers. In particular, they exhibit veryhigh tensile and tear strength, high flexibility at low temperatures,extremely good abrasion and scratch resistance. They also have a highstability against oil, fats and many solvents, as well as stabilityagainst UV radiation and are being employed in a number of end useapplications such as the automotive and the footwear industry.

As a result of the increased demand for lighter materials, a low densityTPU needs to be developed which, in turn, represents a big technicalchallenge to provide, at minimum, equal physical properties toconventional low density PU.

It is already known to produce soles and other parts of polyurethane bya polyaddition reaction of liquid reactants resulting in an elasticsolid moulded body. Up till now the reactants used were polyisocyanatesand polyesters or polyethers containing OH-groups. Foaming was effectedby adding a liquid of low boiling point or by means of CO₂, therebyobtaining a foam at least partially comprising open cells.

Reducing the weight of the materials by foaming the TPU has not givensatisfactory results up to now. Attempts to foam TPU using well-knownblowing agents as azodicarbonamides (exothermic) or sodiumhydrocarbonate(endothermic) based products were not successful for mouldings withreduced densities below 800 kg/m³.

The present invention thus concerns a process for the preparation offoamed thermoplastic polyurethanes whereby the foaming of thethermoplastic polyurethane is carried out in the presence of thermallyexpandable microspheres and in the presence of an additional blowingagent, said microspheres containing a hydrocarbon.

By using exothermic blowing agents, a lower density foam (down to 750kg/m³) with very fine cell structure can be achieved but the surfacefinish is not acceptable for most applications and demould time is evenlonger.

From the above it is clear that there is a continuous demand for lowdensity TPUs having improved skin quality which can be produced withreduced demould times.

It has now been surprisingly found that foaming TPUs in the presence ofthermally expandable microspheres, allows to meet the above objectives.Demould times are significantly reduced and the process can be carriedout at lower temperatures, resulting in a better barrel stability. Inaddition, the use of microspheres even allows to further reduce thedensity while maintaining or improving the skin quality and demouldtime.

The present invention thus concerns a process for the preparation offoamed thermoplastic polyurethanes whereby the foaming of thethermoplastic polyurethane is carried out in the presence of thermallyexpandable microspheres.

The low density thermoplastic polyurethanes thus obtained (density notmore than 800 kg/m³) have a fine cell structure, very good surfaceappearance, a relatively thin skin and show comparable physicalproperties to conventional PU which renders them suitable for a widevariety of applications.

The invention provides TPU products having outstanding low temperaturedynamic flex properties and green strength at the time of demould, atdensity 800 kg/m³ and below.

The term “green strength”, as is known in the art, denotes the basicintegrity and strength of the TPU at demould. The polymer skin of amoulded item, for example, a shoe sole and other moulded articles,should possess sufficient tensile strength and elongation and tearstrength to survive a 90 to 180 degree bend without exhibiting surfacecracks. The prior art processes often require 5 minutes minimum demouldtime to attain this characteristic.

In addition, the present invention therefore provides a significantimprovement in minimum demould time. That is to say, a demould time of 2to 3 minutes is achievable.

The use of microspheres in a polyurethane foam has been described inEP-A 29021 and U.S. Pat. No. 5,418,257.

Adding blowing agents during the processing of TPUs is widely known, seee.g. WO-A 94/20568, which discloses the production of foamed TPUs, inparticular expandable, particulate TPUs, EP-A 516024, which describesthe production of foamed sheets from TPU by mixing with a blowing agentand heat-processing in an extruder, and DE-A 4015714, which concernsglass-fibre reinforced TPUs made by injection moulding TPU mixed with ablowing agent.

Nevertheless, none of the prior art documents discloses the use ofthermally expandable microspheres to improve the skin quality of foamedlow density TPU (density 800 kg/m³ and even below) nor do thesedocuments suggest the benefits associated with the present invention.

DETAILED DESCRIPTION

Thermoplastic polyurethanes are obtainable by reacting a difunctionalisocyanate composition with at least one difunctional polyhydroxycompound and optionally a chain extender in such amounts that theisocyanate index is between 90 and 110, preferably between 95 and 105,and most preferably between 98 and 102.

The term ‘difunctional’ as used herein means that the averagefunctionality of the isocyanate composition and the polyhydroxy compoundis about 2.

The term “isocyanate index” as used herein is the ratio ofisocyanate-groups over isocyanate-reactive hydrogen atoms present in aformulation, given as a percentage. In other words, the isocyanate indexexpresses the percentage of isocyanate actually used in a formulationwith respect to the amount of isocyanate theoretically required forreacting with the amount of isocyanate-reactive hydrogen used in aformulation.

It should be observed that the isocyanate index as used herein isconsidered from the point of view of the actual polymer forming processinvolving the isocyanate ingredient and the isocyanate-reactiveingredients. Any isocyanate groups consumed in a preliminary step toproduce modified polyisocyanates (including such isocyanate-derivativesreferred to in the art as quasi- or semi-prepolymers) or any activehydrogens reacted with isocyanate to produce modified polyols orpolyamines, are not taken into account in the calculation of theisocyanate index. Only the free isocyanate groups and the freeisocyanate-reactive hydrogens present at the actual elastomer formingstage are taken into account.

The difunctional isocyanate composition may comprise any aliphatic,cycloaliphatic or aromatic isocyanates. Preferred are isocyanatecompositions comprising aromatic diisocyanates and more preferablydiphenylmethane diisocyanates.

The polyisocyanate composition used in the process of the presentinvention may consist essentially of pure 4,4′-diphenylmethanediisocyanate or mixtures of that diisocyanate with one or more otherorganic polyisocyanates, especially other diphenylmethane diisocyanates,for example the 2,4′-isomer optionally in conjunction with the2,2′-isomer. The polyisocyanate component may also be an MDI variantderived from a polyisocyanate composition containing at least 95% byweight of 4,4′-diphenylmethane diisocyanate. MDI variants are well knownin the art and, for use in accordance with the invention, particularlyinclude liquid products obtained by introducing carbodiimide groups intosaid polyisocyanate composition and/or by reacting with one or morepolyols.

Preferred polyisocyanate compositions are those containing at least 80%by weight of 4,4′diphenylmethane diisocyanate. More preferably, the4,4′-diphenylmethane diisocyanate content is at least 90, and mostpreferably at least 95% by weight.

The difunctional polyhydroxy compound used has a molecular weight ofbetween 500 and 20000 and may be selected from polyesteramides,polythioethers, polycarbonates, polyacetals, polyolefins, polysiloxanes,polybutadienes and, especially, polyesters and polyethers, or mixturesthereof. Other dihydroxy compounds such as hydroxyl-ended styrene blockcopolymers like SBS, SIS, SEBS or SIBS may be used as well.

Mixtures of two or more compounds of such or other functionalities andin such ratios that the average functionality of the total compositionis about 2 may also be used as the difunctional polyhydroxy compound.For polyhydroxy compounds the actual functionality may e.g. be somewhatless than the average functionality of the initiator due to someterminal unsaturation. Therefore, small amounts of trifunctionalpolyhydroxy compounds may be present as well in order to achieve thedesired average functionality of the composition.

Polyether diols which may be used include products obtained by thepolymerisation of a cyclic oxide, for example ethylene oxide, propyleneoxide, butylene oxide or tetrahydrofuran in the presence, wherenecessary, of difunctional initiators. Suitable initiator compoundscontain 2 active hydrogen atoms and include water, butanediol, ethyleneglycol, propylene glycol, diethylene glycol, triethylene glycol,dipropylene glycol, 1,3-propane diol, neopentyl glycol, 1,4-butanediol,1,5-pentanediol, 1,6-pentanediol and the like. Mixtures of initiatorsand/or cyclic oxides may be used.

Especially useful polyether diols include polyoxypropylene diols andpoly(oxyethylene-oxypropylene) diols obtained by the simultaneous orsequential addition of ethylene or propylene oxides to difunctionalinitiators as fully described in the prior art. Random copolymers havingoxyethylene contents of 10–80%, block copolymers having oxyethylenecontents of up to 25% and random/block copolymers having oxyethylenecontents of up to 50%, based on the total weight of oxyalkylene units,may be mentioned, in particular those having at least part of theoxyethylene groups at the end of the polymer chain. Other usefulpolyether diols include polytetramethylene diols obtained by thepolymerisation of tetrahydrofuran. Also suitable are polyether diolscontaining low unsaturation levels (i.e. less than 0.1 milliequivalentsper gram diol).

Other diols which may be used comprise dispersions or solutions ofaddition or condensation polymers in diols of the types described above.Such modified diols, often referred to as ‘polymer’ diols have beenfully described in the prior art and include products obtained by the insitu polymerisation of one or more vinyl monomers, for example styreneand acrylonitrile, in polymeric diols, for example polyether diols, orby the in situ reaction between a polyisocyanate and an amino- and/orhydroxyfunctional compound, such as triethanolamine, in a polymericdiol.

Polyoxyalkylene diols containing from 5 to 50% of dispersed polymer areuseful as well. Particle sizes of the dispersed polymer of less than 50microns are preferred.

Polyester diols which may be used include hydroxyl-terminated reactionproducts of dihydric alcohols such as ethylene glycol, propylene glycol,diethylene glycol, 1,4-butanediol, neopentyl glycol,2-methylpropanediol, 3-methylpentane-1,5-diol, 1,6-hexanediol orcyclohexane dimethanol or mixtures of such dihydric alcohols, anddicarboxylic acids or their ester-forming derivatives, for examplesuccinic, glutaric and adipic acids or their dimethyl esters, sebacicacid, phthalic anhydride, tetrachlorophthalic anhydride or dimethylterephthalate or mixtures thereof.

Polyesteramides may be obtained by the inclusion of aminoalcohols suchas ethanolamine in polyesterification mixtures.

Polythioether diols which may be used include products obtained bycondensing thiodiglycol either alone or with other glycols, alkyleneoxides, dicarboxylic acids, formaldehyde, amino-alcohols oraminocarboxylic acids.

Polycarbonate diols which may be used include those prepared by reactingglycols such as diethylene glycol, triethylene glycol or hexanediol withformaldehyde. Suitable polyacetals may also be prepared by polymerisingcyclic acetals.

Suitable polyolefin diols include hydroxy-terminated butadiene homo- andcopolymers and suitable polysiloxane diols include polydimethylsiloxanediols.

Suitable difunctional chain extenders include aliphatic diols, such asethylene glycl, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,2-propanediol, 2-methylpropanediol, 1,3-butanediol,2,3-butanediol, 1,3-pentanediol, 1,2-hexanediol,3-methylpentane-1,5-diol, diethylene glycol, dipropylene glycol andtripropylene glycol, and aminoalcohols such as ethanolamine,N-methyldiethanolamine and the like. 1,4-butanediol is preferred.

The TPUs suitable for processing according to the invention can beproduced in the so-called one-shot, semi-prepolymer or prepolymermethod, by casting, extrusion or any other process known to the personskilled in the art and are generally supplied as granules or pellets.

Optionally, small amounts, i.e. up to 30, preferably 20 and mostpreferably 10, wt % based on the total of the blend, of otherconventional thermoplastic elastomers such as PVC, EVA or TR may beblended with the TPU.

Any thermally expandable microspheres can be used in the presentinvention. However, microspheres containing hydrocarbons, in particularaliphatic or cycloaliphatic hydrocarbons, are preferred.

The term “hydrocarbon” as used herein is intended to includenon-halogenated and partially or fully halogenated hydrocarbons.

Thermally expandable microspheres containing a (cyclo)aliphatichydrocarbon, which are particularly preferred in the present invention,are commercially available. Such microspheres are generally dry,unexpanded or partially unexpanded microspheres consisting of smallspherical particles with an average diameter of typically 10 to 15micron. The sphere is formed of a gas proof polymeric shell (consistinge.g. of acrylonitrile or PVDC), encapsulating a minute drop of a(cyclo)aliphatic hydrocarbon, e.g. liquid isobutane. When thesemicrospheres are subjected to heat at an elevated temperature level(e.g. 150° C. to 200° C.) sufficient to soften the thermoplastic shelland to volatilize the (cyclo)aliphatic hydrocarbon encapsulated therein,the resultant gas expands the shell and increases the volume of themicrospheres. When expanded, the microspheres have a diameter 3.5 to 4times their original diameter as a consequence of which their expandedvolume is about 50 to 60 times greater than their initial volume in theunexpanded state. An example of such microspheres are the EXPANCEL-DUmicrospheres which are marketed by AKZO Nobel Industries of Sweden(‘EXPANCEL’ is a trademark of AKZO Nobel Industries).

A blowing agent is added to the system, which may either be anexothermic or endothermic blowing agent, or a combination of both. Mostpreferably however, an endothermic blowing agent is added.

Any known blowing agent used in the preparation of foamed thermoplasticsmay be used in the present invention as blowing agents.

Examples of suitable chemical blowing agents include gaseous compoundssuch as nitrogen or carbon dioxide, gas (e.g. CO₂) forming compoundssuch as azodicarbonamides, carbonates, bicarbonates, citrates, nitrates,borohydrides, carbides such as alkaline earth and alkali metalcarbonates and bicarbonates e.g. sodium bicarbonate and sodiumcarbonate, ammonium carbonate, diaminodiphenylsulphone, hydrazides,malonic acid, citric acid, sodium monocitrate, ureas, azodicarbonicmethyl ester, diazabicylooctane and acid/carbonate mixtures. Preferredendothermic blowing agents comprise bicarbonates or citrates.

Examples of suitable physical blowing agents include volatile liquidssuch as chlorofluorocarbons, partially halogenated hydrocarbons ornon-halogenated hydrocarbons like propane, n-butane, isobutane,n-pentane, isopentane and/or neopentane.

Preferred endothermic blowing agents are the so-called ‘HYDROCEROL’blowing agents as disclosed in a.o. EP-A 158212 and EP-A 211250, whichare known as such and commercially available (‘HYDROCEROL’ is atrademark of Clariant).

Azodicarbonamide type blowing agents are preferred as exothermic blowingagents.

Microspheres are usually used in amount of from 0.1 to 5.0 parts byweight per 100 parts by weight of thermoplastic polyurethane. From 0.5to 4.0 parts by weight per 100 parts by weight of thermoplasticpolyurethane of microspheres are preferred. Most preferably,microspheres are added in amounts from 1.0 to 3.0 parts by weight per100 parts by weight of thermoplastic polyurethane.

The total amount of blowing agent added is usually from 0.1 to 5.0 partsby weight per 100 parts by weight of thermoplastic polyurethane.Preferably, from 0.5 to 4.0 parts by weight per 100 parts by weight ofthermoplastic polyurethane of blowing agent is added. Most preferably,blowing agent is added in amounts from 1.0 to 3.0 parts by weight per100 parts by weight of thermoplastic polyurethane.

Additives which are conventionally used in thermoplastics processing mayalso be used in the process of the present invention. Such additivesinclude catalysts, for example tertiary amines and tin compounds,surface-active agents and foam stabilisers, for examplesiloxane-oxyalkylene copolymers, flame retardants, antistatic agents,plasticizers, organic and inorganic fillers, pigments and internal mouldrelease agents.

The foamed thermoplastic polyurethanes of the present invention can bemade via a variety of processing techniques, such as extrusion,calendering, thermoforming, flow moulding or injection moulding.Injection moulding is however the preferred production method.

The presence of thermally expandable microspheres allows for a reductionin processing temperatures. Typically the process of the presentinvention is carried out at temperatures between 150 and 175° C.

Advantageously, the mould is pressurised, preferably with air, and thepressure is released during foaming. Although such process is known andcommonly available from several machine producers, it has beensurprisingly found that conducting the process of the present inventionin a pressurised mould results in TPU articles having an excellentsurface finish and physical properties, while having an even furtherreduced density (down to 350 kg/m³).

Thermoplastic polyurethanes of any density between about 100 and 1200kg/m³ can be prepared by the method of this invention, but it isprimarily of use for preparing foamed thermoplastic polyurethanes havingdensities of less than 800 kg/m³, more preferably less than 700 kg/m³and most preferably less than 600 kg/m³.

The thermoplastic polyurethane is customarily manufactured as pelletsfor later processing into the desired article. The term ‘pellets’ isunderstood and used herein to encompass various geometric forms, such assquares, trapezoids, cylinders, lenticular shapes, cylinders withdiagonal faces, chunks, and substantially spherical shapes including aparticle of powder or a larger-size sphere. While thermoplasticpolyurethanes are often sold as pellets, the polyurethane could be inany shape or size suitable for use in the equipment used to form thefinal article.

According to another embodiment of the present invention, thethermoplastic polyurethane pellet of the present invention comprises athermoplastic polyurethane body, the thermally expandable microspheresand a binding agent which binds the body and the microspheres. Thebinding agent comprises a polymeric component that has an onsettemperature for its melt processing lower than the onset temperature ofthe melt processing range of the TPU. The pellets may also includeblowing agents and/or additive components such as colorant or pigments.

The binding agent covers at least part of the thermoplastic polyurethanebody. In a preferred embodiment, the thermoplastic polyurethane body andmicrospheres are substantially encapsulated by the binding agent. By‘substantially encapsulated’ we mean that at least three-quarters of thesurface of the thermoplastic polyurethane body is coated, and preferablyat least about nine-tenths of the resin body is coated. It isparticularly preferred for the binding agent to cover substantially allof the polyurethane body and microspheres. The amount of binding agentto the thermoplastic polyurethane may typically range from at leastabout 0.1% by weight and up to about 10% by weight, based on the weightof the thermoplastic polyurethane pellet. Preferably, the amount of thebinding agent is at least about 0.5% by weight and up to 5% by weight,based on the weight of the thermoplastic polyurethane pellet.

Preferably, the binding agent has an onset temperature for its meltprocessing range that is below the onset temperature of the meltprocessing range of the thermoplastic polyurethane body. Thus thebinding agent may be applied as a melt to the thermoplastic polyurethanebody composition while the latter is a solid or substantially a solid.The onset temperature of the melt processing range ot the binding agentis preferably above about 20 degree C., and more preferably it is above60 degree C., and even more preferably it is at least about 80 degree C.The onset temperature of the melt processing range of the polymericcomponent of the coating preferably has an onset temperature for itsmelt processing range at least about 20 degree C. and even morepreferably at least about 40 degree C. below, the onset temperature forthe melt processing range of the thermoplastic polyurethane body. If thecustomized thermoplastic polyurethane pellets are to be dried using adryer, then the melt processing range of the binding agent is preferablyabove the temperature of the dryer. In a preferred embodiment, thebinding agent is chosen to prevent or slow water absorption so that adrying step before forming the desired article is unnecessary.

The binding agent may then be added to the TPU pellets by severaldifferent methods. In one method, the pellets are placed in a containerwith the coating composition while the pellets are still at atemperature above the onset temperature of the melt processing range ofthe binding agent. In this case the binding agent may be already meltedor may be melted by the heat of the pellets or by heat appliedexternally to the container. For example, without limitation, thebinding agent may be introduced to the container as a powder when it isto be melted in the container. The binding agent can be any substancecapable of binding the thermoplastic polyurethane body and themicrospheres. Preferably the binding agent comprises a polymericcomponent. Examples of suitable polymeric components includepolyisocyanates and/or prepolymers thereof.

The foamed thermoplastic polyurethanes obtainable via the process of thepresent invention are particularly suitable for use in any applicationof thermoplastic rubbers including, for example, footwear or integralskin applications like steering wheels.

Customized thermoplastic polyurethanes may be produced more efficientlyusing the process according to the present invention. The customizedthermoplastic polyurethanes may be formed into any of the articlesgenerally made with thermoplastic resins. Examples of articles areinterior and exterior parts of automobiles, such as inside panels,bumpers, housing of electric devices such as television, personalcomputers, telephones, video cameras, watches, note-book personalcomputers; packaging materials; leisure goods; sporting goods and toys

In another embodiment, the present invention concerns a reaction systemcomprising (a) a TPU and (b) thermally expandable microspheres.

The invention is illustrated, but not limited, by the following examplesin which all parts, percentages and ratios are by weight.

EXAMPLES Example 1 (Comparative)

TPU pellets (Avalon 62AEP; ‘Avalon’ is a trademark of Imperial ChemicalIndustries Ltd.) were dry blended with an endothermic blowing agent (1%NC175 powder or 2% INC7175ACR (which is a masterbatch equivalent); bothsupplied by Tramaco GmbH).

The dry blend was then processed on an injection moulding machine (DesmaSPE 231) to form a test moulding of dimensions 19.5*12.0*1 cm.

The processing temperatures for all the examples can be seen on Table 1.The physical properties obtained for all the examples can be seen onTable 2. Abrasion was measured according to DIN53516.

Example 2 (Comparative)

The TPU of example 1 was dry blended with an exothermic blowing agent(Celogen AZNP130; available from Uniroyal) and was processed in the sameway as in Example 1.

The minimum achievable density to avoid severe surface marking is 1000kg/m³ with an addition level of 0.3%.

Example 3 (Comparative)

The TPU of example 1 was dry blended with a mixture of an exothermic andan endothermic blowing agent (0.3% Celogen AZNP130 and 0.7% NC175) andprocessed in the same way as Example 1.

Example 4 (Comparative)

The TPU of example 1 was dry blended with 4% of thermally expandablemicrospheres (Expancel 092 MB 120; commercially available from AkzoNobel). This blend was processed in the same way as Example 1.

Example 5

The TPU of example 1 was dry blended with 2% of thermally expandablemicrospheres (Expancel 092 MB120) and an endothermic blowing agent (1%NC175 or 2% INC7175ACR) and processed in the same way as Example 1.

Example 6

The TPU of example 1 was dry blended with 2% of thermally expandablemicrospheres (Expancel 092 MB120) and 1% of an exothermic blowing agent(Celogen AZNP130). Again this was processed in the same way as Example1.

Example 7

The TPU of example 1 was dry blended with 2% of thermally exandablemicrospheres (Expancel 092 MB120), 0.7% of an endothermic blowing agent(NC175) and 0.3% of an exothermic blowing agent (Celogen AZNP130). Againthis was processed in the same way as Example 1.

Example 8

The TPU of example 1 was dry blended with 2% of thermally expandablemicrospheres (Expancel 092 MB120) and an endothermic blowing agent (1%NC175 or 2% INC7175ACR). This was processed on a Main Group injectionmoulding machine.

Example 9

The TPU of example 1 was dry blended with 2.0% of thermally expandablemicrospheres (Expancel 092 MB 120) and 2% of an exothermic blowing agent(IM7200; commercially available from Tramaco GmbH). This dry blend wasprocessed on a Main Group machine with an air injection system (SimplexS16).

Example 10

The TPU of example 1 was dry blended with 2.5% of thermally expandablemicrospheres (EXP 092 MB120) and 2% of an exothermic blowing agent(IM7200). This dry blend was processed on a Main Group machine with anair injection system (Simplex S16).

TABLE 1 Processing Temperatures of Injection Moulding Zone 1 Zone 2 Zone3 Nozzle Mould Temp. (C.) Ex. 1* 180 185 190 185 50 Ex. 2* 175 180 185180 50 Ex. 3* 180 185 190 185 50 Ex. 4 155 160 165 160 50 Ex. 5 160 165170 165 50 Ex. 6 160 165 170 165 50 Ex. 7 160 165 170 165 50 Ex. 8 155160 165 160 40 Ex. 9 155 160 165 160 25 Ex. 10 155 160 165 160 25*comparative example

TABLE 2 Properties Hard- Flex. ness Abra- Resistance Demould SkinDensity (Shore sion (No. of time Appear- (kg/m³) A) (mg) cycles)(seconds) ance Ex. 1* 810 61 53 >100.000 180 Excellent Ex. 2* 750 6170 >100.000 210 Bad Ex. 3* 800 61 60 >100.000 180 Good Ex. 4 800 68120 >100.000 120 Excellent Ex. 5 700 58 105 >100.000 130 Excellent Ex. 6670 57 130 >100.000 150 Good Ex. 7 700 58 110 >100.000 130 Excellent Ex.8 550 51 125 >100.000 180 Excellent Ex. 9 450 46 105 >100.000 180Excellent Ex. 10 350 40 125 >100.000 180 Excellent *comparative example

Example 11

Example 11 provides for TPU pellets comprising microspheres formulatedwith binding agent. TPU pellets were pre-heated in a hot air oven at100° C. Then as a binding agent, an isocyanate prepolymer based onDaltorez® P321 and Suprasec® MPR is prepared at 80° C. The binding agent(1–2% by weight) is then mixed into the TPU pellets to fully wet thesurface of the TPU. The additives are then added and mixing continuesuntil a homogeneous distribution of the additives on the surface of theTPU pellets is achieved. This mixture is then discharged into apolythene container and cooled to 10° C. to allow the coating tosolidify. This ‘cake’ is then de-agglomerated by hand and is ready foruse in the injection molding machine.

These coated pellets were processed on the injection molding machine andsuccessfully blown to densities of 0.73 g/cc.

Daltorez®P321 is a polyester based polyol based on adipic acid and 1,6hexanediol Suprasec® MPR is pure MDI

1. Foamable thermoplastic polyurethane pellet comprising a preformedthermoplastic polyurethane body and thermally expandablehydrocarbon-containing microspheres, at least the thermoplasticpolyurethane body being substantially encapsulated by a binding agentcomprising a polyisocyanate or prepolymer thereof having an onsettemperature for its melt processing which is lower than the onsettemperature for the melt processing range of the thermoplasticpolyurethane.
 2. Foamable thermoplastic polyurethane pellet according toclaim 1 wherein said polyurethane is the reaction product ofdifunctional isocyanate with at least one difunctional polyhydroxycompound.
 3. Foamable thermoplastic polyurethane pellet according toclaim 1, further comprising an additional blowing agent.
 4. Foamedthermoplastic polyurethane obtained by foaming the foamablethermoplastic polyurethane pellet of claim
 3. 5. Foamable thermoplasticpolyurethane pellet according to claim 1, wherein thehydrocarbon-containing microspheres contain an aliphatic orcycloaliphatic hydrocarbon.
 6. Foamable thermoplastic polyurethanepellet according to claim 1, wherein the thermoplastic polyurethanepellets are made by reacting a difunctional isocyanate compositioncomprising an aromatic difunctional isocyanate with at least onedifunctional polyhydroxy compound.
 7. Foamable thermoplasticpolyurethane pellet according to claim 6, wherein the aromaticdifunctional isocyanate comprises diphenylmethane diisocyanate. 8.Foamable thermoplastic polyurethane pellet according to claim 7, whereinthe diphenylmethane diisocyanate comprises at least 80% by weight of4,4′-diphenylmethane diisocyanate.
 9. Foamable thermoplasticpolyurethane pellet according to claim 6, wherein the difunctionalpolyhydroxy compound comprises a polyoxyalkylene diol or polyester diol.10. Foamable thermoplastic polyurethane pellet according to claim 9,wherein the polyoxyalkylene diol comprises oxyethylene groups. 11.Foamable thermoplastic polyurethane pellet according to claim 10,wherein the polyoxyalkylene diol is a poly(oxyethylene-oxypropylenediol).
 12. Foamable thermoplastic polyurethane pellet according to claim1, wherein the amount of the hydrocarbon-containing microspheres isbetween 0.5 and 4.0 parts by weight per 100 parts by weight ofthermoplastic polyurethane.
 13. Foamable thermoplastic polyurethanepellet according to claim 12, wherein the amount of thehydrocarbon-containing microspheres is between 1.0 and 3.0 parts byweight per 100 parts by weight of thermoplastic polyurethane. 14.Foamable thermoplastic polyurethane pellet according to claim 3, whereinthe blowing agent is an endothermic blowing agent.
 15. Foamablethermoplastic polyurethane pellet according to claim 14, wherein theendothermic blowing agent comprises bicarbonates or citrates. 16.Foamable thermoplastic polyurethane pellet according to claim 3, whereinthe blowing agent is an exothermic blowing agent.
 17. Foamablethermoplastic polyurethane pellet according to claim 16, wherein theexothermic blowing agent comprises azodicarbonamide type compounds. 18.Foamable thermoplastic polyurethane pellet according to claim 3, whereinthe amount of the blowing agent is between 0.5 and 4.0 parts by weightper 100 parts by weight of thermoplastic polyurethane.
 19. Foamablethermoplastic polyurethane pellet according to claim 18, wherein theamount of the blowing agent is between 1.0 and 3.0 parts by weight per100 parts by weight of thermoplastic polyurethane.
 20. Foamedthermoplastic polyurethane according to claim 4 which is carried out byinjection molding.
 21. Foamed thermoplastic polyurethane according toclaim 4 which is carried out in a pressurized mold.
 22. Foamedthermoplastic polyurethane according to claim 4 having a density notmore than 700 kg/m³.
 23. Foamed thermoplastic polyurethane according toclaim 4 having a density of not more than 600 kg/m³.